Systemic Apicomplexans

(part 2)Neospora and

Sarcocystis

Grouped by Infection Site and Morphology

systemic

intestines

blood/tissue

Flagellates(sg = Excavates)

HemoflagellatesTrypanosoma cruzi

Tritrichomonas foetus

Leishmania infantum

Giardia spp.

Mucoflagellates

Trypanosoma cruziLeishmania infantum

Intestinal apicomplexa

Blood apicomplexa (piroplasmidia)

Cryptosporidium parvum (gregarine)Eimeria spp. (coccidia)

Cystoisospora spp. (coccidia)

Cytauxzoon felisBabesia spp.

Toxoplasma gondiiNeospora caninumSarcocystis spp.

Systemic apicomplexa (coccidia)

Parasitic Protozoa Apicomplexa

(sg =Alveolates)

Neospora caninum• Canine coccidian

• Complex Life Cycles

• Bovine abortion

https://homesteadontherange.com

• Canine neurologic disease

Morphology: Neospora caninum Oocyst

Small, sub-spherical, smooth coat, no polar cap, single embryo when passed = unsporulated (sporulate after 1-3 days)

Sporulated oocyst contains 2 sporocysts with 4 sporozoites each = 8 sporozoites total

https://www.researchgate.net/figure/8663822_fig2_Fig-2-PCR-for-Neospora-caninum-and-Hammondia-heydorni-using-DNA-extracted-from-oocysts

Morphology:Neospora caninumBradyzoite cyst (cysts found in tissue); facilitate persistent infection

www.cmgm.stanford.edu

www.k-state.edu

Obligate Indirect Life Cycle

Definitive Host = canids

Trans-generational infection

Intermediate Host = herbivores (cattle)

Obligate Indirect Life Cycle: N. caninum

Canids

Obligate Indirect Life Cycle (heteroxenous) Definitive host – Canids only (Dog, Coyote, Wolf, etc.) Intermediate Host (IH) – Cattle and other animals

Transmission -- carnivorism, ingestion of tissue cysts from aborted cattle fetus

Invasion -- Zoites excyst from tissue cyst and invade enterocytes Asexual reproduction (enterocytes and other cells)

endodyogeny AND merogony

intermediate host definitive host

Sexual reproduction (only occurs in canids) in enterocytes Gametogony, Macrogamete, Microgamete, Exflagellation, Fertilization,

Zygote, Oocyst formation. Dissemination

Oocysts (unsporulated) exit the canid in the feces and contaminate the environment ~ 4 days post ingestion → sporulate after 1-3 days

Canids (definitive hosts) are the only hosts to pass oocysts Oocysts highly resistant and remain infectious for many months.

Obligate Indirect Life Cycle: N. caninumCanids

definitive host

Transmission / Invasion (details) After ingestion of cow tissue cyst

Intestinal Some zoites infect intestinal cells to complete sexual cycle oocyst

in the feces Systemic

Other zoites go to deeper tissue and go through asexual cycles → tachyzoites become tissue cysts with bradyzoites (predilection for neural tissue).

Congenital If dog is pregnant, zoites → transplacental to puppies.

definitive host Obligate Indirect Life Cycle: N. caninumCanids

Transmission - Cattle ingest sporulated oocysts from canid feces

intermediate hostdefinitive host

Obligate Indirect Life Cycle: N. caninum

Cattle

Invasion Intestinal – sporozoites penetrate intestinal lining

(no replication and invasion of enterocytes)

Systemic - zoites move to extra-intestinal cells → asexual replication tachyzoites (fast replication and transform into bradyzoites) bradyzoite (slow replication, form tissue cysts in neural, muscle, myocardial,

placenta, fetus)

Congenital Transmission - zoites → transplacental to infect calf

Complex Life Cycle: N. caninumCattle

Congenital Transmission (details)

Infected fetus aborts in 2nd or 3rd trimester, or born early, impaired

Infected fetus survives, passes infection on to offspring = Trans-generational infection Cows infected in utero will in-turn infect their calves, without reinfection

from sporocyst in dog feces These calves are usually seropositive and less likely to have abortions

OR

intermediate host intermediate host

intermediate host

“re-activated” bradyzoites invade the placenta and fetus

Ingest sporulated oocyst from dog

intermediate host

Complex Life Cycle: N. caninumcow-to-cow (Congenital Neosporosis)

(bradyzoites)

Dog-to-dog via sporulated oocysts -has not been reported Sporulated oocyst ingestion does not result in oocyst production FYI: If ingested, the parasite may go systemic & transplacental (not

Intestinal) –like intermediate host

Dog-to-dog via transplacental (bitch to puppies)

Complex Life Cycle: N. caninumDog-to-Dog

Intestinal phase = no pathology(only in canids)

Extra-intestinal phase = systemic disease (occurs in canids or intermediate hosts)

Explosive multiplication of tachyzoites massive direct destruction of host cells acute immune response

Tissue cysts w/ bradyzoites may cause tissue damage; low inflammation; latent “Re-activation” source for transplacental transmission

Pathogenesis: N. caninum

More commonly a neuromuscular disease of puppies after transplacental infection (congenital neospora)

Adults usually subclinical but may develop dz Neuromuscular dz = muscle atrophy, rigid

hyperextension, paralysis, head tilt, gait abnormality, dysphagia, seizure

Other non-specific clinical signs: nodular dermatitis, pneumonia, urine incontinence, fecal incontinence, nephritis, myocarditis, polymyositis

Clinical Disease: N. caninumDogs

rigid hyperextensionhttp://www.vin.com/apputil/content/defaultadv1.aspx?meta=Generic&pId=11157&id=3857014

Congenital Neosporosis Litter-mates dying with signs of

polyradiculitis (inflammation of the nerve roots, especially of the hind limbs)

Puppy with signs of paralysis of the rear limbs at 3-8 weeks of age (ascending paralysis)

Puppy with flaccid hind limb paresis

Clinical Disease: N. caninumPuppies

Abortions (10-20% of abortions caused by N. caninum)

Abortions usually occur with 1st post-infection pregnancy; autolysis of fetus

Later pregnancies usually go to term, but calves are infected (maintenance of dz in herds)

Trans-generational infections Seropositive calves give birth to seropositive

calves – without reinfection via sporocyst ingestion ↓ milk production and ↓ weight gain

https://www.cityu.edu.hk/ph/en/Research/VDP.html

Clinical Disease: N. caninumCattle

http://genex.crinet.com/page4393/AbortionInDairyCattleGeneralConcepts

Cattle Abortions

Diagnosis: N. caninum Dogs

Puppy – classic flaccid hind limb Serology, molecular tests-PCR Organism on biopsy, necropsy of litter

mates

Cattle Diagnostic arrays for multiple abortion

infectious agents Serology and molecular tests-PCR Antibody tests for whole milk

https://www.koofers.com/flashcards/cpb-exam-2-egglist-add-ons/review

cyst filled with bradyzoites

Dogs No drugs available to kill tissue forms

Cattle No drug therapy available

Treatment: N. caninum

Epidemiology, Control & ZoonosisN. caninum

Epidemiology -worldwide Risk factors = presence of dogs on farms and

dairy production (dairy cattle) Control

Limit cattle exposure to wild and domestic canid populations

Cull seropositive cows? Cull cows with midterm abortions?

Don’t let dogs have access to raw meat, offal or dead animals

Not Zoonotic

Sarcocystis cruzi

• Complex Life Cycle

• Canine coccidian

• Causes disease in cattle

Morphology: Sarcocystis cruzi Sporocyst (identified in feces, not oocyst)

Thin-walled oocyst sporulates and ruptures before exiting in the feces, thus sporocysts are seen in the feces

small, oval, smooth coat, no polar cap; 4 sporozoites

Morphology: Sarcocystis cruzi Sarcocysts (bradyzoites in muscles cysts)

zoites find their way to muscle tissue, where they go through schizogony and form sarcocysts.

Infective to the definitive, carnivorous host Facilitate persistent infection (immune system doesn’t clear)

The Korean Journal of Parasitology 2018; 56(2): 121-127.

Obligate Indirect Life Cycle Definitive Host =

canids, other carnivores

Intermediate Host = cattle

Obligate Indirect Life Cycle (heteroxenous) Definitive host – Canids (Dog, Coyote, Wolf, etc.), raccoons Intermediate Host – Cattle

Transmission carnivorism, ingestion of sarcocysts (bradyzoites inside a

muscle cysts) in cattle Invasion

Bradyzoites invades intestinal cells → gamatogony begins NO ASEXUAL reproduction occurs in the dog

Indirect Life Cycle: Sarcocystis cruziCanids

Sexual reproduction only occurs in dogs Gametogony, Macrogamete, Microgamete, Exflagellation, Fertilization,

Zygote, Oocyst Formation The oocyst sporulates within the gut lumen, then ruptures, releasing its 2

sporocysts into the gut lumen

Indirect Life Cycle: Sarcocystis cruziCanids

Dissemination Sporocysts exit the host in the feces and contaminate the environment Dogs are the only hosts to pass sporocysts. Sporocysts are infectious when shed, are very resistant and remain

infectious for several months if kept cool and moist.

Asexual reproduction – occurs in vascular endothelial cells and muscle cells Merozoites → merogony (schizogony), then disperse throughout to muscle cells Bradyzoites replicate form sarcocysts (slow process, over months) Sarcocysts (muscle cysts), full of bradyzoites develop within muscle cells and remain

viable for the life of the intermediate host.

Indirect Life Cycle: Sarcocystis cruziCattle

Transmission ingestion of a sporocyst from canid feces

Invasion Sporozoites cross intestines and enter vascular endothelial cells

Pathogenesis: S. cruzi Intestinal Phase in Canids – no pathology.

Systemic Disease in Cattle Direct destruction vascular endothelial cells and muscle

cells Acute immune response Multi-system DZ due to zoites throughout the vascular

endothelium and muscles, w/ immune reaction and inflammation that follows

Systemic Sarcocystosis -- cattle only Protracted fever, lymphadenopathy,

anorexia, cachexia, muscle spasms, myositis, hyper-excitability, diarrhea, hyper-salivation, weakness, hair loss around eyes, neck and tail switch (“rat-tail”), prostration, death

Sporadic abortions, still births

Pathology in cattle begins about 4-6 weeks post-ingestion of sporocysts

Immune status of the host and the dose of sporocysts determine clinical disease.

Clinical Disease: S. cruzihttp://old.iss.it/binary/crlp/cont/Fayer_Sarcocystis.pdf

Dogs – sporocysts on a routine fecal exam

Cattle – serology, necropsy

Diagnosis: S. cruzi

https://capcvet.org/guidelines/coccidia/

Cystoisospora spp.

Cystoisospora spp.

Neospora andToxoplasma

Sarcocystis

Cryptosporidium

Sarcocystis sporocystin dog feces

Sarcocyst in Muscle (histology/gross)

http://praca-w-niemczech.info/imalsdrm-sarcocystis.html

https://www.merckvetmanual.com/musculoskeletal-system/sarcocystosis/overview-of-sarcocystosis

Sarcocystis aucheniae in Llama

Treatment: S. cruzi Dogs

None – not necessary

Cattle Amprolium may provide some prophylactic

protection Treatment against sarcocysts is ineffective

Epidemiology, Control & ZoonosisS. cruzi

Epidemiology: distributed worldwide in cattle

Control: wild and domestic canid populations

Don’t let dogs have access to raw meat, offal or dead animals

Not Zoonotic

Sarcocystis neurona

• Sylvatic Life Cycle

• Opossum coccidan

• Causes Equine Protozoal Myeloencephalitis (EPM)

© Gregorita Ko

http://www.baltimorepestanimal.com/opossumdisease.html

DO

I: http://dx.doi.org/10.1645/GE-230R

Morphology: Sarcocystis neurona Sporocyst (not Oocyst)

Thin-walled oocyst sporulates and ruptures before exiting in the feces, thus sporocysts are seen in opossum feces

small, oval, smooth coat, no polar cap; 4 sporozoites

DOI: http://dx.doi.org/10.1645/GE-230R

Intact oocyst sporocyst

Sarcocystis neurona

https://veteriankey.com/common-equine-diseases/

Mature sarcocysts are essential for the completion of the life cycle.

Sarcocysts do not develop in the horse.

Obligate Indirect Life Cycle: S. neurona

Sylvatic (wild animals)

Life Cycle: S. neuronaSylvatic (wild animals)

Obligate Indirect Life Cycle (heteroxenous) Definitive host (DH) – Opossum (North and South American) Intermediate Host (IH) – other small mammals and birds

Transmission Opossum (DH) ingests sarcocyst in muscle of IH IH ingests sporocysts from opossum feces

Accidental host – horse ingest sporocyst from opossum feces Asexual stages in tissue, disseminates throughout body,

especially neural tissue (merozoites and schizonts detected) Systemic disease

Pathogenesis: S. neurona Intestinal Phase in Opossum – no pathology.

Systemic Disease in Horses a predilection for neural tissue (neurons and leukocytes

of the brain and spinal cord) Zoites cause destruction of host cells, and acute immune

response / inflammation (meronts and merozoites seen in neurons)

FYI: other protozoa (T. gondii, N. caninum, others may cause EPM-like symptoms in horses)

Clinical Disease: S. neurona Equine Protozoal Myeloencephalitis (EPM)

Spinal Cord involvement Gait abnormalities, unilateral muscle

atrophy (gluteal), myopathy, asymmetric weakness, and ataxia

Demarcated spontaneous sweating, loss of reflexes, cutaneous hyper-sensation.

Cranial nerve involvement Seizures, visual deficits, behavioral

abnormalities Brain involvement

Depression, head tilt, facial paralysis, muscle atrophy (masseter), dysphagia

Without treatment, may progress to recumbencyand death

http://www.sciencedirect.com/science/article/pii/S0304401700003848#FIG2

Sarcocystis neuronaAtaxia

http://www.sciencedirect.com/science/article/pii/S0304401715000448

Sarcocystis neuronaMuscle atrophy

Diagnosis: S. neuronaHorses

Observation of Clinical Signs Mostly neurologic and muscle atrophy. There is a broad spectrum of disease agents that induce

similar clinical signs Serology (CSF and serum)

Serology Antibody IgG against S. neurona indicates exposure; may also give a

false-positive (cross-reactivity to another non-pathogenic Sarcocystis species)

Seropositive + neurological clinical signs strongly supportive of EPM Paired serology testing using CSF and serum more predicative of active

disease Western Blotting and ELISAs use S. neurona specific antigens → less cross

reactivity

Diagnosis: S. neuronaHorses

PCR detects S. neurona DNA = current infection

Post-mortem demonstration of organism in CNS lesions.

Sarcocystis neuronaNecropsy / Histology

http://www.sciencedirect.com/science/article/pii/S0304401715000448

http://www.sciencedirect.com/science/article/pii/S0304401700003848#FIG2

https://tvmdl.tamu.edu/2018/03/16/equine-protozoal-myeloencephalitis-epm-diagnosed-horse/

EPM Treatment Ponazuril, diclazuril, pyrimethamine, sulfadiazine.

Long treatment period (6-8 wks). Be vigilant of side-effects.

Anti-inflammatories; supportive care

Improvement in 60-70%, complete recovery in up to 20%, relapse in 20% (not likely to clear organism)

Epidemiology, Control & Zoonosis: S. neurona

Epi: confined to the Americas (opossum Didelphis virginianaand D. albiventris distribution) estimated ~50% of all horses in US have been exposed to S. neurona <1% develop disease

Control: prevent access of opossums to horse-feeding / watering areas

Fallen fruit should be removed from horse pastures. Why?

Zoonosis: no reports of human infections Infection in dogs, cats and sea mammals (otters) reported

See Review Table: Systemic ProtozoaPosted on-line at Parasitology Website:

https://parasitology.cvm.ncsu.edu/vmp930/lecture.html

The information in the review tables is basic information that you should know. You should also be able to use that information via critical thinking to answer more complex case-based questions.

What you’re expected to know